Colorectal cancer (CRC) is the second leading cause of cancer deaths in the United States. The five-year survival rate is high (90 percent) following treatment of American Joint Committee on Cancer (AJCC) stage I CRC but decreases substantially as disease progresses to stage II (75 percent) and stage III (50 percent). Hence, the presence of lymph node metastasis is one of the most important prognostic factors. Approximately one-third of patients initially diagnosed with AJCC stage I or II CRC develop systemic disease despite "negative" lymph nodes. This implies that these patients have occult nodal or systemic disease not detected by current techniques. Previous studies have demonstrated that lymph node micrometastases documented by ultrastaging correlate with poorer survival. Because the average CRC resection specimen contains 15 or more lymph nodes, the utilization of ultrastaging techniques on each lymph node would be labor and cost intensive. Therefore, a means of focusing an examination on the lymph nodes most likely to contain metastases would be advantageous. Our hypothesis is that inaccurate pathology analysis (i.e. the presence of occult metastasis in CRC regional lymph nodes) may account for the stage I or II patients that will develop systemic disease. To address this problem, improved methods for regional node sampling, pathology analysis, and metastatic disease detection are needed. JWCI developed the sentinel lymph node (SLN) technique to improve staging and reduce unnecessary lymph node dissections in patients with melanoma and breast cancer. More recently, novel molecular techniques and molecular markers were developed in our laboratory ad have been applied to increase the detection of micrometastases. We have successfully demonstrated the SLN technique in a pilot study with 80 CRC patients. Additionally, we have identified molecular markers in colon cancer cell lines, tumor tissue and lymph nodes from patients in the pilot study. A larger scale study will provide the statistical significance needed to ultrastage patients with colon cancer and determine which patients may be at risk for recurrence. The specific aims of this proposal are: 1) to determine the accuracy and sensitivity of intraoperative lymph node mapping and SLN biopsy in patients with CRC; 2) to evaluate molecular and immunohistochemical methods of detection of micrometastases in the SLN; and, 3) to evaluate the clinicopathological utility of ultrastaging in predicting disease recurrence. This proposed approach may ultimately improve the selection of patients for adjuvant therapy following resection of early-stage colon cancer.